The present invention is concerned with a process for the preparation of 5-formylaminopyrimidines from the corresponding 5-nitrosopyrimidines by reductive formylation.
The hydrogenation of substituted 5-nitrosopyrimidines according to various methods is known. As large scale process, noble metal-catalysed hydrogenation with hydrogen under pressure is usually employed. Thus, for example, to DE-PS 36 38 635, there is described the catalytic hydrogenation of 2,4-diamino-6-hydroxy-5-nitrosopyrimidine (DAHNP) and the reaction of the 2,4,5-triamino-6-hydroxypyrimidine (TAHP) thereby obtained with formic acid to give 2,4-diamino-5-formylamino-6-hydroxypyrimidine (DAFHP). The reaction is carried out in aqueous solution at a temperature of from 20.degree. to 80.degree. C. and at a hydrogen pressure of from 1.4 to 21 bar in the presence of known hydrogenation catalysts. Over the course of the reaction period, 0.8 to 1.5 mol of base must be added continuously per mol of DAHNP. In the case of this reduction method, it is disadvantageous that, on the one hand, a high hydrogen pressure is used, which makes necessary the use of expensive autoclaves or of loop reactors, and, on the other hand, the addition of equimolar amounts of bases for dissolving the starting compound gives rise to an additional amount of salt resulting in a burdening of the environment.
DE-OS 37 27 508 describes the reduction of 5-nitrosopyrimidine derivatives with sodium dithionite and subsequent formylation to give the corresponding 5-formylaminopyrimidines. This method has the disadvantage that, besides the liberation of sulphur dioxide, large amounts of sulphur-containing salts are also obtained as by-products so that the economic efficiency necessary for a technical production is not obtained.
Therefore, it is an object of the present invention to provide a process for the preparation of 5-formylaminopyrimidines from the corresponding 5-nitrosopyrimidines which does not suffer from the above-mentioned disadvantages of the prior art but rather permits, in an economically meaningful and environmentally acceptable way, under pressureless conditions, the conversion of substituted 5-nitrosopyrimidines into 5-formylaminopyrimidines.